I know this is a long post but please take the time if you have it.
Thank You
Part One,
Friends vehicle had intermittent charge system warning light. On inspection noticed junk positive terminal and replaced.
Part Two,
Few months later friend informed me that vehicle had to be started with a jump pack and shut down electric loads on the system to get him home.
Part three,
The PRELIMINARY repair steps.
A. removed battery from the vehicle full charge and test reviled good battery.
B. drove vehicle 10 miles to my place to start diagnostic.
C. I consulted with my alternator expert and supplier about this alternator and we discussed possible issues and parts availability. Because I did not have the alternator in hand we could not pinpoint the regulator possibly needed. Being old school in some respects I removed alternator to get it on the test bench without any other tests on vehicle. (I have been burnt by hairline cracks and bad solder joints inside alternators before and always inspect them.
D. I cracked the case for my own curiosity and nothing seemed problematic with visual inspection. I took it to the alternator shop and it was determined to be a good unit.
E. Alternator installed and no problems for several minutes / miles. them it acted up.
The HARD CORE diagnosis begins.
A. Hooked the the unit up to a proper scanner and monitored GENCOM and GENMON everything looked good scanner reported no issues or faults. I am no good with multiple numbers flashing on the screen that are an attempted to describe a wave form (this is a problem with me not the equipment or information delivery technique) I hooked up the oscilloscope to the GENCOM and GENMON and got proper wave forms. GENMON showed consistent frequency PWM and GENCOM showed consistant frequency PWM bursts when load characteristics changed. We also reset the BMS. So scanner shows no codes, no circuit faults and the wave forms look good!
B. Believing that we had fallen victim to plug corrosion or seating I happily took out for a test drive monitoring the voltage with a simple OBD code reader. Everything was good till it stopped charging and threw warnings.
C. The next day I hooked my bench top analogue scope to the scope to the GENCOM and GENMON using 10x probes in order not to affect the circuit I was measuring. (I only have access to the multi thousand dollar scanner during limited times by the grace of the auto mechanics school in my area.) Again the wave forms were excellent but I got lucky enough that I could force the system to fail with time and heavy load. (turned on AC and brights at idle). At this point one wave form flat lined on the rail (full on no PWM) and the other just chopped at %50 percent duty cycle and maybe 1 volt. In this abusive loading situation I would not expect the alternator to stop charging I would expect the alternator to give all it could and throw a battery light. And the fact is that it stops charging during driving RPMs as well.
D. So this is a intermittent issue. I hooked the vehicle up to a high quality scanner and ran a system health check and it implied a P0620-00 GEN CONTROL error without the PCM actually throwing the code. With this information I ran the ShopKeyPro Pinpoint TestC: DTC P0620 which led me through the point to point wiring harness tests faults to ground and faults to Voltage tests. Shorted the GENMON and GENCOM and tested that there duty cycle stayed within %5 (this was a clever test) Used an actual bulb test light to make sure Vref could handle current at the alternator plug. Also per test instructions wiggled, pulled and poked all connections. Could not get this thing to give a bad reading. what a way to spend a Friday night. DTC
E. My shop time was over for the week. I drove the Edge back to my place it erred out on the way so we had not gotten lucky by re seating the connections (PCM and Alternator) The next day I procured a different factory Ford / Mitsubishi alternator from a Ford edge so no voltage regulator incompatibility problems, installed it. I only started the car long enough to make sure it was charging.
So here I am Sunday morning about to go see if it is fixed. If It is not I don't know where to go except change out PCM and that means new car as this one is not worth it. I'd hate to give that advice when I am simply missing something.
Thank you
Jeremy
